At the moment is appears that Rally waits for all parallel tasks to complete before continuing. For some workloads, e.g. when one wants to index a specific number of documents and run periodic queries while doing so, I can be difficult to ensure that these parallel tasks terminate at roughly the same time.

It would be useful if it was possible to specify which of the parallel tasks that should be considered for termination, e.g. through a flag on the task. The default for all tasks would be that they are considered and at least one of the tasks need to be considered.